9 August 2016 Implementation and performance of the metrology system for the multi-object optical and near-infrared spectrograph MOONS
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The Multi-Object Optical and Near-infrared Spectrograph (MOONS) will cover the Very Large Telescope's (VLT) field of view with 1000 fibres. The fibres will be mounted on fibre positioning units (FPU) implemented as two-DOF robot arms to ensure a homogeneous coverage of the 500 square arcmin field of view. To accurately and fast determine the position of the 1000 fibres a metrology system has been designed. This paper presents the hardware and software design and performance of the metrology system. The metrology system is based on the analysis of images taken by a circular array of 12 cameras located close to the VLTs derotator ring around the Nasmyth focus. The system includes 24 individually adjustable lamps. The fibre positions are measured through dedicated metrology targets mounted on top of the FPUs and fiducial markers connected to the FPU support plate which are imaged at the same time. A flexible pipeline based on VLT standards is used to process the images. The position accuracy was determined to ~5 μm in the central region of the images. Including the outer regions the overall positioning accuracy is ~25 μm. The MOONS metrology system is fully set up with a working prototype. The results in parts of the images are already excellent. By using upcoming hardware and improving the calibration it is expected to fulfil the accuracy requirement over the complete field of view for all metrology cameras.
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Holger Drass, Holger Drass, Leonardo Vanzi, Leonardo Vanzi, Miguel Torres-Torriti, Miguel Torres-Torriti, Rolando Dünner , Rolando Dünner , Tzu-Chiang Shen, Tzu-Chiang Shen, Francisco Belmar, Francisco Belmar, Lousie Dauvin, Lousie Dauvin, Tomás Staig, Tomás Staig, Jonathan Antognini, Jonathan Antognini, Mauricio Flores, Mauricio Flores, Yerko Luco, Yerko Luco, Clémentine Béchet, Clémentine Béchet, David Boettger, David Boettger, Steven Beard, Steven Beard, David Montgomery, David Montgomery, Stephen Watson, Stephen Watson, Alexandre Cabral, Alexandre Cabral, Mahmoud Hayati, Mahmoud Hayati, Manuel Abreu, Manuel Abreu, Phil Rees, Phil Rees, Michele Cirasuolo, Michele Cirasuolo, William Taylor, William Taylor, Alasdair Fairley, Alasdair Fairley, "Implementation and performance of the metrology system for the multi-object optical and near-infrared spectrograph MOONS", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99088E (9 August 2016); doi: 10.1117/12.2232654; https://doi.org/10.1117/12.2232654

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